Wetlands are defined as lands transitional between terrestrial and aquatic systems, where the water table is usually at or near the surface or the land is covered by shallow water. For this classification, wetlands must have one or more of the following three attributes: (l) at least periodically, the land supports mainly hydrophytes (aquatic plants), (2) the substrate is mainly undrained hydric (moist) soil, and (3) the substrate is saturated with water or covered by shallow water at some time during the growing season each year.
Wetlands are an important part of Duluth's natural resources, providing habitat, reducing downstream flooding, and improving water quality. Duluth is fortunate to have retained many of the wetlands that existed here before city development in the mid-1800s. Wetlands are abundant in the St. Louis River upstream of the Duluth-Superior harbor, and in level areas that are "over the hill" above Skyline Drive. See for yourself here. Wetlands have always been uncommon on Duluth's steeper hillslopes, such as the Lincoln Park, Central and East Hillside, Congdon Park, Endion, Lakeside and Lester River areas. Wetlands were formerly more abundant within the Duluth-Superior harbor, but many were destroyed by dredging to deepen the waterway. Sometimes new wetlands were created with the dredge "spoils," such as Southworth Marsh on Park Point.
The National Wetland Inventory (NWI) classification scheme defines wetlands according to the "Classification of Wetlands and Deepwater Habitats of the United States," a system that describes wetlands by soils, hydrology, and vegetation.
Here is one example of how the NWI system works:
In this case "P" stands for Palustrine, "EM" for Emergent, "2" for non-persistent, a water regime of "F" means "semipermanent". Also, there is also the special modifier of "b" which means beaver impounded. You will find this type of wetland in the Hartley Nature Area just upstream of the main pond. Here is that example.
This system uses a hierarchical classification scheme that divides wetlands into five major systems, of which only three can be found in the Duluth area: Palustrine, Lacustrine, and Riverine.
[P] Palustrine - The Palustrine System includes all nontidal wetlands dominated by trees, shrubs, emergents, mosses or lichens, and all such wetlands that occur in tidal areas where salinity due to ocean derived salts is below 0.5 ppt.
[L] Lacustrine - The Lacustrine System includes wetlands and deepwater habitats with all of the following characteristics: 1. situated in a topographic depression or a dammed river channel; 2. lacking trees, shrubs, persistent emergents, emergent mosses or lichens with greater than 30% areal coverage. 3. total area exceeds 8 hectares ( 20 acres ).
(1) Limnetic - Extends outward from Littoral boundary and includes all deep-water habitats within the Lacustrine System.
(2) Littoral - All wetland habitats in the Lacustrine System. Extends from shoreward boundary to 2 meters (6.6 feet) below annual low water or to the maximum extent of nonpersistent emergents, if these grow at depths greater than 2 meters.
Here is a graphic which shows the relationship between these two major systems.